This invention relates to fuel cells and, more particularly, to cells which consume gaseous or liquid fuels and produce electrical energy.
An advantageous fuel cell for energy conversion is described in U.S. Pat. No. 4,863,813 (for which a reissue application, Ser. No. 552,800, was filed on July 13, 1990). In a cell of the type described therein, a hydrogen-containing material at room temperature, such as a gaseous mixture of hydrogen and oxygen, is directly converted to direct-current electrical energy and the only reaction product is water.
In one specific illustrative such cell, a submicrometer-thick gas-permeable ionically conducting membrane made of pseudoboehmite is deposited on an electrode that comprises a platinized impermeable substrate. This membrane constitutes the solid electrolyte of the cell. A layer, of platinum for example, is deposited on the top surface of the membrane to form the second electrode of the cell. The entirety of the second electrode is sufficiently porous (permeable) to allow the gas mixture to pass therethrough.
For a hydrogen/air mixture, such a cell provides useful current at an output voltage as large as about one volt, independent of the ratio of hydrogen to air for hydrogen&gt;50%. In practice, the efficiency of such a cell in converting the fuel mixture to electrical energy is impaired by a side reaction that occurs on the permeable electrode. In this side reaction, which accounts for about 90% of the fuel inefficiency of the cell, hydrogen and oxygen combine to form water. Only heat is produced in this side reaction. Nothing is thereby contributed to the electrical output of the cell.
Fuel efficiency is the single most important parameter that must be improved to upscale a basic cell of the aforespecified type to higher power levels. Such improvement would of course significantly increase the applications for which the cell would be regarded as an attractive energy source.